A material evaporated from a fuel, a lubricant (engine oil), or the like contained in an exhaust gas (a gas phase) discharged from an engine is stuck to a turbine (a vane section and a housing) of a turbocharger installed at an exhaust path of the engine. Then, in a surface (a metal) of the turbine, a carbonization reaction caused by a stuck organic compound (a fuel or a lubricant) progresses, and an inorganic compound (caused by an antioxidant or a detergent dispersant) contained in a fuel or a lubricant is deposited. When deposits (coking deposits) of a carbon material (a material composed of carbon or a carbonized inorganic substance) are generated at a vane section (an impeller) of the turbine, the impeller is unbalanced. As a result, since vibrations are generated from the impeller and a clearance quantity between the impeller and the housing is decreased, the turbine may be damaged or rotational efficiency may be decreased.
In order to remove the coking deposits generated as described above from the turbine, a method of performing a water jet is employed. However, since the coking deposits generated by the material contained in such a gas phase have high hardness, it is impossible for the water jet to obtain a high removal effect.
Here, it can be considered that a certain treatment is performed on the surface of the turbine (the vane section and the housing) to prevent generation of the deposits in advance. A technique for plating chrome (Cr) on a metal surface (for example, Patent Document 1) has been proposed as a technique for preventing eduction of carbon to a metal surface in contact with a liquid containing hydrocarbon when the liquid flows. Patent Document 1 discloses a technique for performing Cr plating to prevent exposure to a metal surface of nickel (Ni) or iron (Fe), which is a catalyst for promoting decomposition of hydrocarbon, in order to prevent eduction of carbon by suppressing decomposition of hydrocarbon in a liquid.
In addition, a technique of coating alumina (Al2O3) on a surface (for example, Patent Document 2) has also been proposed. Patent Document 2 discloses a technique for coating Al2O3, which does not promote an oxidation reaction, rather than manganese (Mn), copper (Cu), platinum (Pt), or palladium (Pd), which is a catalyst for promoting an oxidation reaction, in order to prevent hydrocarbon, fatty acid, or the like, from being stuck to an object surface by suppressing the oxidation reaction and promoting vaporization and evaporation from the surface.